Eosinophil cationic protein (ECP) also known as ribonuclease 3 is a basic protein located in the eosinophil primary matrix. In humans, the eosinophil cationic protein is encoded by the RNASE3 gene. ECP is released during degranulation of eosinophils. This protein is related to inflammation and asthma because in these cases, there are increased levels of ECP in the body. There are three glycosolated forms of ECP and consequently ECP has a range of molecular weights from 18-22 kDa. Eosinophil cationic protein and the sequence related eosinophil-derived neurotoxin (RNASE2) are both members of the Ribonuclease A superfamily. Both proteins possess neurotoxic, helmintho-toxic, and ribonucleo-lytic activities. Eosinophil cationic protein is localized to the granule matrix of the eosinophil. Eosinophil granulocytes appear in large numbers in inflammation sites and in response to certain parasitic infections. These cytoplasmic granules contain positively charged proteins that characterize the cells. ECP is one of the four highly basic proteins that enter the surrounding tissues when activated eosinophils degranulate. There are several mechanisms that can be combined to generate an asthma attack, including specific IgE antibodies, activated inflammatory cells, neurogenic mechanisms, hyperresponsiveness and individual hormonal imbalances. Allergic reactions in the lung typically have two phases. The late phase typically occurs several hours after exposure, upon which eosinophils accumulate in the bronchus and release granule proteins that cause bronchial irritability.